1. Field of the Invention
The present invention relates to a method for bonding a flexible printed circuit (FPC) cable to an ink jet print head assembly, and an apparatus adopting the method.
2. Description of the Related Art
In an ink jet head adopting an electro-thermal transducing technique to discharge ink droplet using bubbles obtained by instantaneously heating ink, a print head die having heaters and nozzles thereon is included. The print head die also includes a plurality of signal lines electrically connected to the heaters, and a plurality of electric contact pads arranged on the peripheral edges of the print head die in an inline configuration in order to allow the signal lines to be coupled to an external circuit.
The pads are connected to FPC cable on which a plurality of conductors corresponding to the pads are arranged side by side. The pads are bonded to the conductors by thermo-sonic bonding.
U.S. Pat. Nos. 4,635,073 and 6,126,271 each disclose a method of bonding the pads to conductors using a thermo-sonic bonding technique. Due to the high vibration energy required for the bonding of each conductor/pad pair, simultaneous bonding of all conductor/pad pairs may have detrimental effect on the integrity of the print head die and any other parts of the ink jet head. Thus, the thermo-sonic bonding technique is a single point bonding method to bond a single conductor to a single pad at a time. In a conventional method shown in FIG. 1, a conductor 3 is brought into contact with a pad 2 installed on a print head die 1, and then a thermo-sonic bonding tool 4 applies pressure and high frequency (ultrasonic) vibration to the conductor 3 one conductor at a time to permanently bond to the pad 2. The remaining pads and conductors are sequentially bonded together one at a time. According to the conventional sequential bonding method, depending on the number of conductor/pad pairs, the bonding process takes a significant amount of time.
In addition, the vibration energy generated by ultrasonic frequency may deform the portion of the conductor 3 where the energy is focused, decreasing the rigidity of the bond, and, as a result, the conductor 3 may easily become separated from the pad.
Moreover, after a conventional bonding process described above, a considerable length of the FPC cable is left to extend above the print head die, which blocks the travel path of a wiper in the maintenance station of the ink jet printing apparatus. Also, when the wiper travels beyond the peripheral boundary of the print head die, the wiper continues to press on the extended portion of the FPC cable, resulting in an unnecessary shear force being applied to the bond between the print head die and the FPC cable.
Furthermore, during a conventional bonding process, the conductor of the FPC cable is completely exposed, i.e., the protective and/or insulation film covering the conductor is completely removed near the bond, requiring an excessive amount of encapsulation over the bond to insulate the exposed upper surface of the conductor. The excessive encapsulation adds height over the bond, and thus also reduces the clearance for a wiper to travel, and increases the distance the ink droplets must travel before landing on the surface of the print medium, e.g., a sheet of paper.